Access to the interior of a forage-holding silo has commonly been through openings in the generally cylindrical wall of the silo. The openings are commonly vertically aligned and separated only by sufficient wall material to support the next higher door structure covering the next higher opening. Ladder rungs have been attached to the outside of known doors in order that a ladder along the outer surface of the silo exists for the purpose of climbing to the openable door immediately above the level of forage in the building. Generally, ladder rungs have been attached to the door itself resulting in a dangerous situation whenever the hinges or some other part of the door becomes worn due to age or disrepair. Thus, with such door assemblies, it is possible that the weight of a person on one of the ladder rungs could cause the hinge or some other portion of the door to yield or otherwise fail and endanger the person.
U.S. Pat. No. 3,997,025 addressed this problem by disclosing an assembly having hinge connecting members function as ladder rungs by extending between the hinge attachment to the door frame structure near one side of the door and the hinge attachment to the door near the other side of the door. A drawback of this system is that the ladder rungs disappear into the interior of the silo when a particular door is opened.
Various silo door latching assemblies have also been known. Most latches close the door sufficiently tight to seal the edges to the door frame. A common latch requires a removable wooden door to be placed between a vertically oriented rod and the door frame. The rod is inserted in openings in the upper and lower frame members. Due to the shape of the rod, when it is rotated approximately 180.degree., it cams the door tightly against the frame.
U.S. Pat. No. 3,997,025 shows another form of latch mechanism. A clamp arm is rotatably attached at its center to the door. At its ends, the clamp arm fits over the frame edges at the outer side of the silo. A pivotal locking bar cams the clamp arm tight thereby pulling the door tight against the inner side of the door frame. A drawback of this mechanism is that any loosening of the wingnut holding the locking bar to the clamp arm results in an easing of the tightness with which the door may be closed and sealed.
The present invention solves these and other problems present in prior art door assemblies.